1. Field of Invention
The present invention relates to shape detection methods and apparatuses for a hot strip mill and, more particularly, to a shape detection device and method used in conjunction with a hot strip reversing mill.
2. Background Art
During the hot rolling of metal strip, such as steel, the rolling process can cause undesirable shape defects in the profile and flatness along the width of the metal strip. This generally results from internal stress differentials within the strip which appear during reduction in a hot strip reversing mill having coiler furnaces on opposite sides. As the need for improved shape is ever present from a mill, techniques are required to ensure the desired shape is achieved during the reduction of the metal strip.
These shape defects can be greatly minimized and often avoided by applying shape control techniques in controlling the rolls of the mill. Shape control techniques include adjustments at the reversing stand of roll bending, screw-down positions, roll shifting and roll cooling. Also, it is important to control the steering of the metal strip between the rolls at the reversing stand to keep the metal strip tracking on mill center.
In order to apply the shape control techniques, the operator must be able to detect when the process is causing the shape defects or when the metal strip tracks off mill center. Currently, the operator visually checks for defects caused by the process and ensures that the metal strip is tracking on mill center. The operator then must adjust the mill manually using the shape control techniques to correct for defects and adjust steering of the metal strip if the metal strip is off mill center.
Pressure transducers and load cells have been used on each side of the reversing stands to detect force differentials between the stand sides to indicate the metal strip is tracking off mill center. The use of pressure transducers or load cells can be unreliable because strip geometry, temperature changes in the metal or hardness of the metal can also cause force differentials that can be detected by the pressure transducers or the load cells.
Today, automated shape control systems using computer technology can control shape of the metal strip with the use of shape detectors. Shape detectors or shape feedback devices detect shape defects throughout the metal strip. The shape control system uses the data from the detector for monitoring and continuously correcting the flatness of the metal strip. The automated shape control system relieves the operator from visually checking for defects and manually making changes to the process. Such systems and shape detectors are described in U.S. Pat. Nos. 3,459,019; 3,688,571; 4,289,005; 4,356,714; 4,428,244; 4,512,170; 4,700,557; 4,809,527; 4,809,528; 4,860,212; 4,964,289; 5,089,776; 5,231,858; 5,267,170; 5,285,684; and 5,400,258.
Shape detectors can be a contact or non-contact shape metering device as discussed in the above-mentioned patents. Each type of shape metering device has the main purpose of detecting shape defects in the metal strip and has been used in cold strip mills and in the finishing train of hot strip mills. Some types of shaper Bring devices can also be used to detect metal strip position and, therefore, can also be used for automatic steering control. One problem that arises is that shape detectors must be incorporated into the design of existing mills. Currently for Steckel and other hot strip reversing mills, an operator still checks for shape defects visually and makes manual adjustments to the mill. Visual detection by an operator is still employed because the mills already in operation are generally restricted to the space available to add a contact or non-contact shape metering device. Although overall space is still a concern with new mills, a new mill can be designed to accommodate shape detectors.
Objects of the present invention are to overcome the drawbacks of the prior art designs and to provide a hot strip reversing mill design which incorporates shape detectors in the most efficient and cost-effective manner.